You should be able to look thru the iron sights and see the dot at the tip of the front sight post. This is called "cowitness."

The real M4 optics fit perfectly on the LM4 rail. The original M68 COO needed the "M4 Spacer" to get the height high enough. Clone "high mount" sights should fit. Note the spacer in these two mounts. (M4 and LM4).

The LM4 and clone Aimpoint CompM4 on top with the included high spacer.
The LWRC M6 with Aimpoint CompM4s on bottom on cantilevered high spacer.

The EoTech milspec 553 is already the correct height. Your EoTech may not be milspec height.

BTW the M4 and M16A4 detachable handles are identical (same part number). This may or may not apply to non-Colt AR15s.